Battery charging device, method for charging battery pack by switching between maximum charging voltage and maximum charging current

ABSTRACT

There is disclosed a battery charging device for charging a battery pack having a battery cell, the battery pack being capable of storing an information for a maximum charging current and a maximum charging voltage of the battery cell and communicating the information with the battery charging device, which includes a communication means for receiving the information indicative of the maximum charging current and the information indicative of the maximum charging voltage of the battery cell which is transmitted from the battery pack, and a control means for controlling charging current and voltage upon charging so as not to exceed the maximum charging current and the maximum charging voltage of the battery cell. Further, in accordance with the present invention, there are disclosed a method for charging the battery pack, and the battery pack capable of being mounted to various electronic apparatuses.

This application is a continuation of Ser. No. 08/827,532 filed Mar. 28,1997.

BACKGROUND OF THE INVENTION

The present invention relates to a battery pack used as a power sourcefor video cameras, portable telephones or personal computers, a batterycharging device for charging the battery pack and a method for chargingthe battery pack.

Hitherto, there are known battery packs constituted by secondarybatteries such as lithium-ion batteries, nickel-cadmium batteries,nickel-hydrogen batteries or the like.

These known battery packs incorporate, for example, a microcomputer forcalculating a residual capacity thereof and conducting communicationswith electronic apparatuses using the battery pack as a power source,peripheral devices, a detection circuit for detecting conditions of abattery cell which are required for the microcomputer to calculate theresidual battery capacity, or the like.

In conventional battery charging devices for these battery packs, forexample, constituted by lithium-ion batteries, there has been used aconstant-voltage charging system in which a predetermined constantvoltage is continuously applied when the battery is charged. Inaddition, the respective battery packs have often been different incharging voltage (which means a maximum charging voltage which can beapplied to the battery pack to be charged, and is hereinafter referredto merely as "maximum charging voltage") per one battery cell dependingupon kinds of electrodes used in the respective battery cells. For thisreason, many of the conventional battery charging devices have been usedonly for charging limited kinds of battery packs compatible thereto.

However, from the standpoint of costs, it have been inconvenient toprepare many battery charging devices compatible to various types ofbattery packs. Accordingly, many of recent battery charging devices areobliged to have such a function by which various types of battery packshaving different maximum charging voltages can be charged.

However, such battery charging devices capable of charging plural kindsof battery packs have been so designed, from the viewpoint of safety, asto operate in conditions for charging the battery packs having thelowermost maximum charging voltage among those of all the compatiblebattery packs. Similarly, the battery charging devices have been sodesigned as to provide such a charging current (which means a maximumcharging current which can flow through the battery pack, and ishereinafter referred to merely as "maximum charging current") identicalto the lowermost maximum charging current among those of all thecompatible battery packs.

Thus, in these conventional battery charging devices, it is impossibleto equally supply an optimum charging energy to all the compatiblebattery packs intended, so that there arise inconveniences that 100%charging cannot be attained or it takes a considerably long time toattain 100% charging.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the afore-mentionedproblems. Accordingly, it is an object of the present invention toprovide a battery charging device capable of supplying an optimumcharging energy to all of a plurality of battery packs intended and amethod for charging the battery pack, and the battery pack which can becharged by such a battery charging device and method.

The battery charging device and method according to the presentinvention are such device and method for charging the battery pack whichcan store at least an information indicative of the maximum chargingcurrent and an information indicative of the maximum charging voltageand communicate the information. In accordance with the presentinvention, the afore-mentioned problems can be overcome by receiving theinformation indicative of the maximum charging current and theinformation indicative of the maximum charging voltage from the batterypack, detecting a current voltage of the battery pack upon charging,changing over a charging condition of the battery pack between aconstant-current charge and a constant-voltage charge depending upon thedetected current voltage, and controlling the charging of the batterypack so as not to exceed the maximum charging current and the maximumcharging voltage.

In addition, the battery pack according to the present inventioncomprises a battery cell, a memory means for storing an informationindicative of a maximum charging current and an information indicativeof a maximum charging voltage of the battery cell and a communicationmeans for transmitting the information indicative of the maximumcharging current and the information indicative of the maximum chargingvoltage, thereby overcoming the afore-mentioned problems.

That is, in accordance with the present invention, it is possible toequally supply an optimum charging energy to all of a plurality ofbattery packs having different maximum charging currents and maximumcharging voltages by storing the information indicative of the maximumcharging current and the information indicative of the maximum chargingvoltage on the battery pack, changing over a charging condition of thebattery pack between a constant-current charge and a constant-voltagecharge depending upon a current voltage of the battery pack when thebattery pack is charged, and further controlling the charging of thebattery pack so as not to exceed the maximum charging current and themaximum charging voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a circuit arrangement of a batterycharging device according to the present invention;

FIG. 2 is a flow chart showing operations of a microcomputerincorporated in the battery charging device when the device is used tocharge a battery pack;

FIG. 3 is a view explaining changing-over operation betweenconstant-current charge and constant-voltage charge;

FIG. 4 is a block diagram showing a specific circuit arrangement of thebattery pack according to the present invention;

FIG. 5 is a flow chart showing a sequence of integrating processing forcomputing charging and discharging currents in the battery packaccording to the present invention;

FIGS. 6A-6C are views explaining the case where the gain G of thecurrent detection circuitry is set so as to satisfy the relation ofq/G=1 mAh/LSB! in the battery pack according to the present invention;and

FIGS. 7A-7C are views explaining the case where the gain G of thecurrent detection circuitry and the like are set so as to satisfy therelation of q/G=8 (2³) mAh/LSB! in the battery pack according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention are described belowby referring to the accompanying drawings.

Referring to FIG. 1, there is schematically shown a system including abattery charging device 100 and a battery pack 1.

In FIG. 1, the battery charging device 100 includes a communicationcircuit 102 for conducting data communication with the afore-mentionedbattery pack 1, a light-emitting element 103 such as a light-emittingdiode, a variable voltage source 104, a variable current source 105, achange-over switch 106 for switching between an output voltage from theafore-mentioned variable voltage source 104 and an output current fromthe afore-metnioned variable current source 105, and a microcomputer101. The microcomputer 101 can control the turning-ON and OFF of theafore-mentioned light-emitting diode 103, the switching of theafore-mentioned change-over switch 106, and a value of the outputvoltage from the afore-mentioned variable voltage source 104 and a valueof the output current from the afore-mentioned variable current source105.

Further, the battery pack 1 includes a battery cell 20 constituted by,for example, a lithium-ion battery, a non-volatile memory 17 for storingat least an information indicative of the maximum charging current ofthe battery cell 20 and an information indicative of the maximumcharging voltage of the battery cell 20, a communication circuit 30 forperforming data communications with the battery charging device 100, anda microcomputer 10. The microcomputer 10 reads out the informationindicative of the maximum charging current and the informationindicative of the maximum charging voltage both stored in thenon-volatile memory 17, and transmits the information to the batterycharging device 100 through the afore-mentioned communication circuit30. In addition, the microcomputer 10 is able not only to recognizevarious conditions of the battery cell 20 such as voltage, current orthe like upon charging in such a manner as described hereinafter, butalso to transmit the information obtained by the recognition to thebattery charging device 100.

A positive terminal TM₊ of the battery pack 1 is coupled with a positiveterminal TM₁₊ of the battery charging device 100. Whereas, a negativeterminal TM₋ of the battery pack 1 is coupled with a negative terminalTM₁₋ of the battery charging device 100. The battery pack 1 is chargedby the battery charging device 100 through these positive and negativeterminals. Further, a control terminal TM_(C) of the battery pack 1 iscoupled with a control terminal TM_(1C) of the battery charging device100, such that the information indicative of the maximum chargingcurrent and the information indicative of the maximum charging voltage,the information for the current or voltage of the battery cell 20 uponcharging, or other information can be communicated, i.e., received andtransmitted, between the battery pack 1 and the battery charging device100.

In this case, as the battery pack 1, there can be used a plurality ofbattery packs which are different in charging voltage (a maximumapplicable charging voltage) per one battery pack and in chargingcurrent (a maximum flowable charging current) per one battery pack, fromeach other depending upon kinds of electrodes used in the respectivebattery cells 20. In the following descriptions, a battery pack having amaximum charging voltage per one battery pack of 4.2 V and a maximumcharging current per one battery pack of 4 A and another battery packhaving a maximum charging voltage per one battery pack of 4.1 V and amaximum charging current per one battery pack of 2 A are used asexamples of the battery packs.

Thus, since there exist plural kinds of battery packs 1, it is requiredthat at least the information indicative of the maximum charging currentand the information indicative of the maximum charging voltage arestored in the afore-mentioned non-volatile memory 17 of each batterypack 1. In this case, the information indicative of the maximum chargingvoltage is constituted by 8 bits where a current per one bit correspondsto 0.1 A, and the information indicative of the maximum charging voltageis constituted by 16 bits where a voltage per one bit corresponds to0.01 V. Incidentally, the reason why 0.01 V is assigned for one bit isthat the difference in maximum charging voltage per one battery cellbetween the respective battery packs are as small as between 4.2 V and4.1 V, and especially in the case of the lithium-ion battery, it isimportant not to exceed the maximum charging voltage upon charging fromthe standpoint of safety.

In the following, there is described the charging operation in which thebattery pack 1 is charged by the battery charging device 100, byreferring to the flow chart as shown in FIG. 2.

First, at the step ST1, the microcomputer 101 of the battery chargingdevice 100 requests the microcomputer 10 of the battery pack 1 totransmit thereto the information indicative of the maximum chargingvoltage and the information indicative of the maximum charging currentboth stored in the non-volatile memory 17. When the informationtransmitted from the battery pack 1 based on the request is received,the microcomputer 101 of the battery charging device 100 can recognizethe maximum charging current permitted to flow through the battery cell20 upon charging and the maximum charging voltage permitted to beapplied to the battery cell 20 upon charging. In addition, when thecharging operation starts, the microcomputer 10 of the battery pack 1recognizes values of currently-charged voltage (current chargingvoltage: CCV) and currently-flowing current of the battery cell 20 asdescribed hereinafter, and transmits to the microcomputer 101 of thebattery charging device 100 the information indicative of thecurrently-charged voltage and currently-flowing current of the batterycell 20, thereby causing the microcomputer 101 of the battery charging100 to recognize these voltage and current values.

Next, at the step ST2, the microcomputer 101 of the battery chargingdevice 100 determines a saturated charging voltage of the battery cell20 based on the information indicative of the maximum charging voltageof the battery pack 1, and calculates a voltage value which correspondsto 90% of the saturated charging voltage. Further, the microcomputer 101compares the current charging voltage of the battery cell 20 transmittedfrom the battery pack 1 with the calculated voltage value corresponding90% of the saturated charging voltage thereof. When it is recognizedthat the current charging voltage is smaller than 90% of the saturatedcharging voltage, the charging program proceeds to the step ST3 wherethe charging of the battery pack 1 is performed in the condition ofconstant-current charge. On the other hand, when it is recognized thatthe current charging voltage is greater than 90% of the saturatedcharging voltage, the charging program proceeds to the step ST7 wherethe battery pack 1 is charged in the condition of constant-voltagecharge. More specifically, when the constant-current charge is performedat the step ST3, the microcomputer 101 of the battery charging device100 changes over the change-over switch 106 to establish the connectionbetween the battery pack 1 and the variable current source 105, and setsa current output from the variable current source 105 to a valuecorresponding to the afore-mentioned maximum charging current, therebypermitting the battery pack 1 to be charged at the set value of thecurrent supplied from the variable current source. However, at thistime, it should be noted that the charging voltage of the battery pack 1does not exceed the maximum charging voltage. On the other hand, whenthe constant-voltage charge is performed at the step ST7, themicrocomputer 101 of the battery charging device 100 changes over thechange-over switch 106 to establish the connection between the batterypack 1 and the variable voltage source 104, and sets a voltage outputfrom the variable voltage source 104 to a value corresponding to theafore-mentioned maximum charging voltage, thereby permitting the batterypack 1 to be charged at the set value of the voltage applied by thevariable voltage source. However, at this time, it should also be notedthat the charging current flowed through the battery pack 1 does notexceed the maximum charging current.

When the constant current charge is performed at the step ST3, themicrocomputer 101 compares the maximum charging current of battery pack1 with the currently-flowing current of the battery cell 20, as shown instep ST4. When it is recognized that the currently-flowing current issmaller than the maximum charging current, the program proceeds to thestep ST5 where the current supplied to the battery pack 1 is increased.On the other hand, when it is recognized that the currently-flowingcurrent is greater than the maximum charging current, the programproceeds to the step ST6 where the current supplied to the battery pack1 is decreased. More specifically, when the current supplied to thebattery pack 1 is increased at the step ST5, the microcomputer 101 ofthe battery charging device 100 controls the variable current source 105to increase a value of the current output therefrom. On the other hand,when the current supplied to the battery pack 1 is increased at the stepST6, the microcomputer 101 of the battery charging device 100 controlsthe variable current source 105 to decrease the value of the currentoutput therefrom.

After the control of the step ST5 or the step ST6 is completed, theprogram for the microcomputer 101 of the battery charging device 100returns to the decision block of the step ST2.

On the other hand, if it is determined in the step ST2 that the currentcharging voltage of the battery pack 1 exceeds 90% of the saturatedcharging voltage so that the constant-voltage charge is to be performedat step ST7, the microcomputer 101 of the battery charging device 100compares the value of the afore-mentioned maximum charging voltage ofthe battery pack 1 with the value of the current charging voltage of thebattery cell 20 transmitted from the battery pack 1, as shown by thestep ST8. If it is determined at the step ST8 that the value of thecurrent charging voltage is smaller than the maximum charging voltage,the voltage applied to the battery pack 1 is intended to be increased bythe microcomputer 101 of the battery charging device 100, as shown inthe step ST9. On the other hand, If it is determined at the step ST8that the value of the current charging voltage is greater than themaximum charging voltage, the voltage applied to the battery pack 1 isintended to be decreased by the microcomputer 101 of the batterycharging device 100, as shown in the step ST10. More specifically, whenthe voltage applied to the battery pack 1 is intended to be increased asin the step ST9, the microcomputer 101 of the battery charging device100 controls the variable voltage source 104 so as to increase a valueof the voltage output therefrom. On the other hand, when the voltageapplied to the battery pack 1 is intended to be decreased as in the stepST10, the microcomputer 101 of the battery charging device 100 controlsthe variable voltage source 104 so as to decrease a value of the voltageoutput therefrom.

After the control of the step ST9 or the step ST10 is completed, theprogram for the microcomputer 101 of the battery charging device 100returns to the execution block of the constant-voltage charge asindicated by the step ST7.

In the meantime, during the time in which it is determined at the stepST2 that the current charging voltage is smaller than 90% of thesaturated charging voltage and therefore the battery pack 1 is chargedin the condition of constant-current charge as in the step ST3 andsubsequent steps, the microcomputer 101 of the battery charging device100 controls the light-emitting diode 103 shown in FIG. 1 so as to keepthe diode turned ON. On the other hand, when it is determined at thestep ST2 that the current charging voltage is greater than 90% of thesaturated charging voltage and therefore the battery pack 1 is chargedin the condition of constant-voltage charge as in the steps ST7 andsubsequent steps, the microcomputer 101 of the battery charging device100 controls the light-emitting diode 103 shown in FIG. 1 so as to keepthe diode turned OFF. As a matter of course, the ON and OFF conditionsof the light-emitting diode 103 may be set reversely. By the provisionof the light-emitting diode, it is possible for user to recognize thecondition that the battery pack 1 is charged up to 90% or more of thesaturated charging voltage.

The microcomputer 101 of the battery charging device 100 performs thecharging operation only during such a period in which the battery pack 1is mounted thereto, and terminates the charging operation when thebattery pack 1 is dismounted therefrom. The detection of mounting ordismounting of the battery pack 1 can be realized, for example, byproviding a sensor for detecting the mounting and dismounting on thebattery charging device 100 and continuously monitoring the output ofthe sensor. Alternatively, the detection of the mounting or dismountingof the battery pack 1 can be determined by detecting interruption of thecommunication between the battery pack 1 and the microcomputer 10.

As described above, in the battery charging device 100 according to thepresent invention, the information indicative of the afore-mentionedmaximum charging current and the information indicative of the maximumcharging voltage stored in the non-volatile memory 17 of the batterypack 1 is read out and the currently-charged voltage and thecurrently-flowing current of the battery pack 1 are also monitoredcontinuously. Further, as shown in FIG. 3, the battery pack 1 is chargedin the condition of constant-current charge in an initial stage of thecharging operation. After the current charging voltage of the batterypack 1 reaches a predetermined voltage (corresponding to 90% of thesaturated charging voltage as indicated by the point P in FIG. 3), thecondition is changed from the constant-current charge to theconstant-voltage charge using the maximum charging voltage. By such anarrangement of the battery charging device 100 according to the presentinvention, it becomes possible to supply an optimum charging energy toall of the battery packs to enable them to be charged up to 100%, and toreduce the time required for achieving the 100% charging condition ofthe battery packs. In general, for example, in the case where two kindsof battery packs one of which has a maximum charging voltage per onebattery cell of 4.2 V and a maximum charging current of 2 A and theother of which has a maximum charging voltage per one battery cell of4.1 V and a maximum charging current of 4 A are charged as describedabove, the one battery pack having a maximum charging current of 4 Arequires a charging current two times that for the other battery packhaving a maximum charging current of 2 A. Accordingly, the formerbattery pack having a maximum charging current of 4 A requires acharging time two times that for the latter battery pack having amaximum charging current of 2 A. However, in accordance with the batterycharging device 100 according to the present invention, the battery packhaving the maximum charging current of 4 A can be supplied with a largeramount of current in the initial stage of the charging operation, sothat it is possible to reduce the charging time required therefor. Also,even though the battery packs have different maximum charging voltagesfrom each other (i.e., one is 4.1 V and the other is 4.2 V), since thecharging condition of each battery pack is changed over to theconstant-voltage charge when the current charging voltage thereofreaches 90% or more of the saturated charging voltage, the battery packcan be charged up to 100% depending upon the maximum charging voltagethereof.

In the afore-mentioned embodiment, the non-volatile memory 17 of thebattery pack 1 can store only the information indicative of the maximumcharging voltage and the information indicative of the maximum chargingcurrent. In addition to the afore-mentioned information, thenon-volatile memory 17 can store the other information indicative ofconnecting conditions of the battery cell 20, for example, the number ofseries connections or, if required, the number of parallel connectionsor the like. For instance, if the information indicative of the numberof series connections is stored in the non-volatile memory 17, thebattery charging device 100 according to the present invention can alsobe used to charge various kinds of battery packs 1 having battery cellswhich are different in number of series connection from each other in anoptimum manner.

Next, a specific arrangement of the battery pack 1 according to thepresent invention is described by referring to FIG. 4.

In the battery pack shown in FIG. 4, the positive electrode of thebattery cell 20 is coupled to the positive terminal TM₊ of the batterypack 1 and the negative electrode of the battery cell 20 is coupled tothe negative terminal TM₋ of the battery pack 1 through acurrent/voltage detection resistance R7.

The microcomputer 10 incorporated in the battery pack 1 is coupled witha power source 16 for microcomputer including series regulators, resetcircuits or the like, and operated by the power supplied from the powersource 16. The charging current detection input terminal DI1 of themicrocomputer 10 is coupled to an output terminal of an operationalamplifier 13, which serves for detecting the charging current. Thedischarge current detection input terminal DI2 is coupled to an outputterminal of the operational amplifier 13, which serves for detecting thedischarge current. In addition, the interrupt input terminal of themicrocomputer 10 is coupled to an output terminal of a NAND gate 15whose two input terminals are coupled to output terminals of operationalamplifiers 13 and 14. The output terminal of the NAND gate 15 is alsocoupled to the power source 16 for microcomputer through a pull-upresistance R8. Besides, the temperature detection input terminal of themicrocomputer 10 is coupled to an output terminal of a temperaturesensor 19 for detecting an ambient temperature of the battery cell 20.The voltage detection input terminal of the microcomputer 10 is coupledto an output terminal of a voltage detection circuit 18 for detecting aterminal voltage of the battery cell 20. The data input terminal of themicrocomputer 10 is coupled to an output terminal of the afore-mentionednon-volatile memory 17. The ground terminal GND of the microcomputer 10is coupled to a negative electrode of the battery cell 20. Thecommunication input and output terminal (SIN and SOUT terminals) of themicrocomputer 10 are coupled to buffer amplifiers 11 and 12,respectively, which constitute a part of the afore-mentionedcommunication circuit 30. Incidentally, the afore-mentioned chargingcurrent input terminal DI1, discharge current input terminal DI2,temperature detection input terminal, voltage detection input terminaland the like are analog input terminals and therefore all areconstituted by A/D input ports. Accordingly, the microcomputer 10incorporates therein an A/D converter for converting these analog inputsinto digital data.

The non-inversion input terminal of the operational amplifier 13 iscoupled to the negative electrode of the battery cell 20 through aresistance R3. The inversion input terminal of the operational amplifier13 is coupled to a negative-feedback resistance R2 for setting anamplification factor and a resistance R1. Accordingly, the voltage fromthe output terminal of the operational amplifier 13 is equal to avoltage value amplified by multiplying a value of the current flowingthrough the battery pack 1 (current flowing upon charging) by a ratio ofa resistance value of the resistance R2 to that of the resistance R1(R2/R1). On the other hand, the non-inversion input terminal of theoperational amplifier 14 is coupled to the negative electrode of thebattery cell 20 through a resistance R6 and a resistance R7 which servesfor detecting current and voltage. The inversion input terminal of theoperational amplifier 14 is coupled to a negative-feedback resistance R5and a resistance R4. Accordingly, the voltage from the output terminalof the operational amplifier 14 is equal to a voltage value amplified bymultiplying a value of the current flowing through the battery pack 1(current flowing upon discharge) by a ratio of a resistance value of theresistance R5 to that of the resistance R4 (R5/R4).

Further, a transistor switch Tr1 is constituted by, for example, a fieldeffect transistor whose gate is coupled to a switching control outputterminal SW1 of the microcomputer 10 and between whose drain and sourcethe afore-mentioned resistance R1 is connected. Accordingly, when thelevel of signal from the switching control output terminal SW1 of themicrocomputer 10 is, for example, HIGH (H), the field effect transistorTr1 is turned ON so that the value of the resistance R1 becomesapproximately zero (namely, only an internal resistance of the fieldeffect transistor Tr1), and the amplification factor (amplifier gain) ofthe operational amplifier 13, whose amplification factor is determinedaccording to the ratio of the value of the resistance R2 to that of theresistance R1 (R2/R1) becomes large. On the other hand, when the levelof signal from the switching control output terminal SW1 of themicrocomputer 10 is, for example, LOW (L), the transistor switch Tr1 isturned OFF so that the amplification factor (amplifier gain) of theoperational amplifier 13 is smaller than the amplification factordetermined according to the ratio of the value of the resistance R2 tothat of the resistance R1 (R2/R1), i.e., the amplification factorobtained in the case where the transistor switch Tr1 is turned ON.Similarly, a transistor switch Tr2 is constituted by, for example, afield effect transistor whose gain is coupled to the switching controloutput terminal SW2 of the microcomputer 10 and between whose drain andsource the afore-mentioned resistance R4 is connected. Accordingly, whenthe level of signal from the switching control output terminal SW2 ofthe microcomputer 10 is, for example, HIGH (H), the transistor switchTr1 is turned ON so that the value of the resistance R4 becomesapproximately zero (namely, only an internal resistance of thetransistor switch Tr2), and the amplification factor (amplifier gain) ofthe operational amplifier 13 becomes large. On the other hand, when thelevel of signal from the switching control output terminal SW2 of themicrocomputer 10 is, for example, LOW (L), the transistor switch Tr2 isturned OFF so that the amplification factor (amplifier gain) of theoperational amplifier 14 becomes small.

In this case, in a normal operational mode (upon running), themicrocomputer 10 continuously monitors the signal levels of theafore-mentioned charging current detection input terminal DI1 anddischarge current detection input terminal DI2. If these levels reachesor exceeds predetermined values, the levels of signals from theafore-mentioned switching control output terminals SW1 and SW2 are bothset to LOW (L) level, so that the transistor switches Tr1 and Tr2 areboth turned OFF, and the amplifier gains of the operational amplifiers13 and 14 becomes small. Accordingly, the microcomputer 10 can measure avalue of the current flowing within the battery pack 1 (current flowingupon charging or discharging) by using the values of outputs from theoperational amplifiers 13 and 14 having the low amplifier gain. For thisreason, the microcomputer 10 can recognize the value of the currentflowing upon charging or discharging so that integrated value ofcharging and discharging currents and the like can be calculated.

On the other hand, in the normal operational mode (upon running), whenthe charging and discharging currents flowing within the battery pack 1are decreased to an extremely small value not more than thepredetermined value, the output value from the operational amplifiers 13and 14, which amplifier gains are both rendered small, also becomessmall. That is, the levels of the afore-mentioned charging currentdetection input terminal DI1 and discharge current detection inputterminal DI2 also becomes small. At this time, in the microcomputer 10,the levels of the afore-mentioned terminals DI1 and DI2 are decreased tolower than the predetermined level. If such a condition is continued fora predetermined period of time, the microcomputer 10 determines that thecircuitry is in a no-load condition, so that the operational modethereof is transferred into a power-saving mode (sleep mode). Upon thepower-saving mode, the circuitry is operated with a lower powerconsumption than in the afore-mentioned normal operational mode, so thatenergy-saving operation thereof becomes possible.

When the microcomputer 10 is operated in the power-saving mode (sleepmode), the levels of signals from the afore-metnioned switching controloutput terminals SW1 and SW2 are both HIGH levels. This causes thetransistor switches Tr1 and Tr2 to be turned ON, so that the amplifiergains of the operational amplifiers 13 and 14 become large. Accordingly,when the circuitry is operated in the power-saving mode (sleep mode),the microcomputer 10 can measure the extremely small current flowingwithin the battery pack 1 (extremely small current flowing upon chargingor extremely small current flowing upon discharge) by using outputvalues of the operational amplifiers 13 and 14 whose amplifier gains arerendered small.

In this case, under such a power-saving operational mode, when thecharging or discharging currents reach or exceed the afore-mentionedpredetermined value, the output values of the operational amplifiers 13and 14 both become large. That is, the levels of the two input terminalsof the afore-mentioned NAND gate 15 are both HIGH levels. Accordingly,the output of the NAND gate 15 becomes a LOW level. Thus, when theoutput level of the NAND gate 15 coupled to the interrupt input terminalbecomes a LOW level, the microcomputer 10 cancels the afore-mentionedpower-saving operational mode so that the operational mode of thecircuitry is transferred from the power-saving operational mode to thenormal operational mode.

As described above, in the circuitry arrangement illustrated in FIG. 4,since the circuitry is operated with a lower power consumption in thepower-saving mode of operation than that in the normal operational mode,considerable power saving can be achieved. In addition, in the circuitryarrangement illustrated in FIG. 4, the microcomputer 10 can perform theON/OFF control of the transistor switches Tr1 and Tr2 by means of theswitching control outputs SW1 and SW2, so that the amplifier gains ofthe operational amplifiers 13 and 14 can be changed over. Theafore-mentioned arrangement makes it possible both to detect anextremely small current in the power-saving operational mode and tomeasure the value of current in the normal operational mode.

The voltage detection circuit 18 is a voltage-dividing resistorconstituted by resistances R9 and R10. By using the voltage-dividingresistor, the terminal voltage of the battery cell 20 can be detected.The voltage value detected by the voltage detection circuit 18 issupplied to the afore-mentioned voltage detection input terminal of themicrocomputer 10. Accordingly, based on the detected voltage valuesupplied from the voltage detection circuit 10 and received by thevoltage detection input terminal of the microcomputer 10, it is possibleto recognize the terminal voltage of the battery cell 20.

In addition, the temperature sensor 19 is constituted by, for example, athermistor for detecting a temperature, or the like, and disposed inclose proximity to the battery cell 20. The temperature value detectedby the temperature sensor 18 is supplied to the temperature detectioninput terminal of the microcomputer 10. Accordingly, the microcomputer10 can recognize the temperature of the battery cell 20 based on thedetected temperature value supplied to the temperature detection inputterminal thereof.

Further, the afore-mentioned non-volatile memory 17 is constituted by,for example, EEP-ROM, and can also store therein data (cycle data)indicative of number of permissible maximum charging and dischargingcycles of the battery cell 20 in addition to the information indicativeof the maximum charging voltage or the maximum charging current and theinformation indicative of the connecting conditions as mentioned above.If such data indicative of the number of maximum permissible chargingand discharging cycles of the battery cell 20 are stored in thenon-volatile memory 17, the microcomputer 10 can transmit a flagindicative of reaching the maximum permissible charging and dischargingcycles to electronic equipment to which the battery pack 1 is mounted,by reading out the data indicative of the number of the maximumpermissible charging and discharging cycles from the non-volatile memory17 and simultaneously measuring current charging and discharging cyclesof the battery cell 20. Accordingly, when the flag transmitted from thebattery pack 1 is received by the electronic equipment, it is possibleto provide, for example, an indication for directing the user'sattention to necessity of replacement of the battery pack, an indicationof a residual capacity of the battery pack, or the like.

Next, there is explained the calculation of residual battery capacityoperated by the afore-mentioned microcomputer 10, that is, theintegrating operation of charging and discharging currents based on theoutput values of the afore-mentioned operational amplifiers 13 and 14.Incidentally, in these operations, the operational amplifiers 13 and 14are used as a charging current detection amplifier or a dischargingcurrent detection amplifier in the current detection circuitry.

The current detection circuitry detects a charging or dischargingcurrent i mA! flowing through the resistance R7 and amplifies thedetected current by a given gain G V/mA! inclusive of that ofcurrent/voltage conversion, so as to output a voltage e=iG V! which isthen supplied to the charging current detection input terminal DI1 andthe discharge current detection input terminal DI2 as A/D ports of themicrocomputer 10. In the A/D converting means (A/D converter) of themicrocomputer 10, the input voltage e V! is quantized with a givenquantization width or step q V/LSB! to convert the analog data into adigital value x=e/q (=iG/q). Based on the digital value x, themicrocomputer 10 performs the calculation every predetermined operationperiod T h: hour!.

Assuming that the current i continuously flows for the operation periodT, the increment or decrement ΔY is given by the formula of ΔY=iT=(xq/G)mAh!. The increment or decrement ΔY is represented by the followingformula, using the digital data x obtained by the afore-mentioned A/Dconversion.

    ΔY=(qT/G)x

When the respective values q, T and G in the above formula are adjustedsuch that the multiplication coefficient qT/G is equal to 2^(n), theabove formula is rewritten as ΔY=(2^(n))x. As a result, the value can bereadily calculated by bit shift.

Meanwhile, a positive (+) value of the current i corresponds to chargingoperations while a negative value (-) of the current i corresponds todischarging operations. In the afore-mentioned embodiment as shown inFIG. 4, among the charging and discharging currents flowing through theresistance R7, the charging current is detected by the operationalamplifier 13 while the discharging current is detected by theoperational amplifier 14. The respective detected charging anddischarging currents are output as a positive voltage and supplied tothe charging current detection input terminal DI1 and the dischargecurrent detection input terminal DI2. Accordingly, assuming that avoltage e₁ is supplied from the operational amplifier 13 to the chargingcurrent detection input terminal DI1 of the microcomputer 10 based on adetected charging currents i₁ and the voltage e₁ is subjected toanalog-to-digital conversion by the A/D converter within themicrocomputer 10 to obtain a digital value x₁, and that a voltages e₂ issupplied from the operational amplifier 14 to the discharging currentdetection input terminals DI2 of the microcomputer 10 based on adetected charging current i₂ and the voltage e₂ is subjected toanalog-to-digital conversion by the A/D converter within themicrocomputer 10 to obtain a digital value x₂, the increment ordecrement ΔY mAh! of the residual battery capacity Y mAh! everyoperational period T can be given by the following formula: ##EQU1##

If the multiplication coefficient is set as qT/G=2^(n), the aboveformula is given by:

    ΔY=(x.sub.1 -x.sub.2) x 2.sup.n

As a result, the value can be readily calculated by bit shift.

FIG. 5 is a flow chart showing a computing operation of themicrocomputer 10 for calculating the residual battery capacity by theintegrating operation of the afore-mentioned charging and dischargingcurrent values.

In FIG. 5, at the step ST41, a residual battery capacity data Y mAh! isset as an initial residual capacity Y₀ mAh!. This procedure isrepresented by Y-Y₀. At the next step ST42, the increment or decrementΔY, that is, (x₁ -x₂) x 2_(n), is added to the residual battery data YmAh! obtained immediately before the initiation of the step. Thethus-obtained added value is stored as a new residual battery capacitydata Y mAh! in an internal memory (not shown) of the microcomputer 10.This procedure is represented by Y- Y+(x₁ -x₂) x 2^(n) !. In the furtherstep ST43, the computing program returns to the step ST41 after waitingfor a predetermined period of time T corresponding to theafore-mentioned operational period.

In this case, when the gain V/mA! inclusive of that of current/voltageconversion in the current detection circuitry, the quantized step qV/LSB! upon analog-to-digital conversion in the microcomputer 10, andthe period for the integrating operation of the charging and dischargingcurrent values by the microcomputer 10 are selected such that therelationship therebetween is represented by qT/G=2^(n), the integratedcurrent values or the residual battery capacity values can be obtainedby bit shift without multiplying the coefficient.

The amplifier gain of the operational amplifier 13 constituting thecurrent detection circuitry is determined by the ratio of R2/R1 asdescribed above, while the amplifier gain of the operational amplifier14 is determined by the ratio of R5/R4 as described above. Further, thecurrent/voltage conversion ratio is determined by the resistance R7. Theamplifier gain of the operational amplifier 13 for detecting a chargingcurrent and the amplifier gain of the operational amplifier 14 fordetecting a discharge current may be same or different. The quantizationstep q of the analog-to-digital conversion of the microcomputer 10 isfixed by the IC in many cases. In addition, the operation period T canbe varied according to software used.

More specifically, for example, assuming that relationships of q/G=2^(k)mA/LSB! and T h!=1/2^(m) h! (where k and m represent integers) areestablished, the increment or decrement ΔY every operation period T isgiven by the formula: ##EQU2##

Accordingly, the residual battery capacity Y mAh! every operation periodT can be renewed by the formula:

    Y- Y+(x.sub.1 -x.sub.2) x 2.sup.k-m !

As a result, the integrating current value can be obtained only by theaddition and subtraction, and by (k-m) bit shift operations.

Specifically, in FIG. 6, there is shown the case where the gain G of theafore-mentioned current detection circuitry is set, for example, suchthat the relation of q/G=1 is established. Although the quantizationstep q is fixed in many cases, the value q may also be variable so as toobtain the relation of q/G=1. At this time, if an initial capacity isset to 8 mAh as shown in FIG. 6(A), the residual battery capacity Y isrepresented by 08H (where H is a hexadecimal numeral. That is, lowerfour bits are given by "1000".). In the case of the initial capacity of08H, for example, when charging of 1 mA per hour is conducted for onehour, the A/D conversion data corresponding to input values of thecharging current detection input terminal DI1 and the discharge currentdetection input terminal DI2 is given by 01H as it is. By adding thisvalue to the initial capacity, a new residual batter capacity data Y of9 mAh is obtained. Therefore, the residual battery capacity data Y isrepresented by 09H (that is, lower four bits are given by "1011".), asshown in FIG. 6(B). Successively, when charging of 2 mA per hour isconducted on the battery having the residual battery capacity of 09H forone hour, a new residual battery capacity data Y amounts to 11 mAh sothat it is represented by 0BH (that is, lower four bits are given by"1011".), as shown in FIG. 6(C). As is understood from the abovediscussion, for example, if the gain G of the afore-mentioned currentdetection circuitry 80 or the like is set so as to establish therelation of q/G=1 mAh/LSB!, the integrating current value can beobtained without multiplication of the coefficient.

Similarly, as shown in FIGS. 7(A) to 7(C), in the case where theafore-mentioned gain and the like are set, e.g., to q/G=8 (=2³)mAh/LSB!, when the initial capacity is, for example, 1 mAh as shown inFIG. 7(A), the residual battery capacity Y is represented by 01H (whereH is a hexadecimal numeral, that is, lower four bits are given by"0001".). In the case of such an initial capacity of 01H, for example,when charging of 8 mA per hour is conducted for one hour, the A/Dconversion data corresponding to input values of the charging currentdetection input terminal DI1 and the discharge current detection inputterminal DI2 is given by 01H as shown in FIG. 7(B). When this data isadded to the afore-mentioned residual battery capacity data Y, it isnecessary to multiply the value by 2³. The multiplication of the data by2³ can be achieved by rightward three bit shift operation, so that anincrement of 08H, i.e., 8 mAh can be obtained. By adding this incrementto the original residual battery capacity data, a new residual batterycapacity data Y of 9 mAh is obtained as shown in FIG. 7(C). As isunderstood from the above discussion, if the gain G of theafore-mentioned current detection circuitry and the like are set, forexample, so as to establish the relation of q/G=8 (2³) mAh/LSB!, theintegrated current value can be obtained without the multiplication ofthe coefficient though only the bit shift operation is required. Ingeneral, if the q/G is set to 2^(n) mAh/LSB!, the integrated currentvalue or the residual battery capacity can be obtained by the n-time bitshift and the addition.

In the foregoing, there is described the embodiment using thelithium-ion battery as a battery cell. However, the present invention isalso applicable to other secondary batteries such as nickel-cadmiumbatteries or nickel-hydrogen batteries in a similar manner.

Further, the battery pack according to the present invention can bemounted to various electronic apparatuses such as video cameras,portable telephones, personal computers or the like.

As described above, in accordance with the present invention, theinformation indicative of the maximum charging current and theinformation indicative of the maximum charging voltage are stored in thebattery pack. Further, the battery pack is charged by the batterycharging device in such a manner that constant-current charge isconducted at an initial stage of the charging and the charging mode ischanged over to constant-voltage charge when the current chargingvoltage of the battery pack exceeds a predetermined value. Thus, bychanging over the charging mode between the constant-current charge andthe constant-voltage charge depending upon the current charging voltageof the battery pack and controlling so as not to exceed the maximumcharging current and the maximum charging voltage, it is possible tosupply an optimum charging energy to all of a plurality of battery packswhich are different in maximum charging current and maximum chargingvoltage from each other.

What is claimed is:
 1. A battery charging device for charging a batterypack having a battery cell, said battery pack being capable of storinginformation indicative of a maximum charging voltage of the battery celland being capable of communicating said information, said batterycharging device comprising:communication means for receiving saidinformation indicative of the maximum charging voltage of the batterycell transmitted from said battery pack; a variable current source forsupplying an output current; a variable voltage source for supplying anoutput voltage; and control means for controlling said variable voltagesource and variable current source to supply said output voltage andcurrent upon charging of said battery pack so as not to exceed saidmaximum charging voltage and said maximum charging current, said controlmeans controlling said variable voltage source and variable currentsource to switch between a constant-current charge using said maximumcharging current and a constant-voltage charge using said maximumcharging voltage.
 2. The battery charging device according to claim 1,wherein said communication means receives a present voltage transmittedfrom said battery pack upon charging.
 3. The battery charging deviceaccording to clam 1, wherein a charged voltage of said battery pack doesnot exceed said maximum charging voltage when the constant-voltagecharge is supplied.
 4. The battery charging device according to claim 1,wherein a charged current of said battery pack does not exceed saidmaximum charging current when the constant-current charge is supplied.5. The battery charging device according to claim 1, further comprisingoutput means for selectively outputting the output voltage from thevariable voltage source or the output current from the variable currentsource, and wherein the control means controls the output means so as tochange an output between the output voltage and the output current. 6.The battery charging device according to claim 1, further comprisinglight-emitting means controlled by said control means such that whenthere is a changeover between the constant-current charge and theconstant-voltage charge, the light-emitting means is turned ON.
 7. Thebattery charging device according to claim 1, further comprisinglight-emitting means controlled by said control means such that whenthere is a changeover between the constant-current charge and theconstant-voltage charge, the light-emitting means is turned OFF.
 8. Amethod for charging a battery pack having a battery cell, said batterypack being capable of storing information for a maximum charging voltageof the battery cell and being capable of communicating said information,said method comprising the steps of:receiving said information for themaximum charging voltage of the battery cell transmitted from saidbattery pack; supplying an output voltage and an output current to saidbattery cell; and controlling the supplied output voltage and currentsuch that the maximum charging current and the maximum charging voltageof the battery cell are not exceeded upon charging, said controllingincluding switching between a constant-current charge using said maximumcharging current and a constant-voltage charge using said maximumcharging voltage.
 9. The method according to claim 8, further comprisingthe steps of:receiving a present voltage during charging transmittedfrom the battery pack; and controlling the battery pack so as to switchbetween said constant-current charge and said constant-voltage charge.10. The method according to claim 8, wherein when the battery pack ischarged by the constant-current charge, the battery pack is controlledsuch that the charged voltage does not exceed the maximum chargingvoltage.
 11. The method according to claim 8, wherein when the batterypack is charged by the constant-voltage charge, the battery pack iscontrolled such that the charged current does not exceed the maximumcharging current.